1. Field of the Invention
The present invention relates to converting the format of image signals from an interlaced scanning to a progressive scanning, and more particularly, to an apparatus and a method for converting to a progressive scanning format which restores the line data missing from each field of an image by analyzing motions of corresponding reference fields of the image.
2. Background of the Related Art
Recently, digital image devices such as digital televisions and DVDs became so popular so that they now coexist with analog image devices such as conventional television systems. Therefore, it is necessary to display analog signals on the digital devices. Generally, the analog TV image signals have an interlaced scanning format, so it is required to increase the scanning or resolution rate of the signals in order to properly display them on a high quality display unit. For that reason, the signals having the interlaced scanning format should be converted to a progressive scanning format.
According to a typical method currently being used for such format transformations, values of pixels corresponding to two lines adjacent to a missing line in a field are analyzed and their average values are being used to estimate values of pixels corresponding to the missing line.
After deciding whether there is any motion of the image by analyzing pixel values of the frame or adjacent field, average values obtained from the corresponding field are used if there is any movement, and otherwise, the pixel values in a prior or next field are used to estimate the missing line. This is because checking an existence of the motion is comparatively simpler than estimating a degree/amount of the motion, and it involves less number of calculations.
However, even if there is any very small amount of the movement in the image, the pixel values must be obtained only from information given from the current field, causing inefficient uses of available information, and the spatial resolution of the screen is reduced so that the display quality is significantly degraded.
As a matter of fact, moving image data are constantly changing, but we can only presume that adjacent picture frames have high correlations to each other, and the levels of such movements are quite insignificant. Therefore, if we are able to utilize not only characteristics of the reference frames, but also amounts of their movements, the resolution of the image can be greatly enhanced while the missing data can be restored with values closer to the actual values.
The conversion to the progressive scanning format utilizing the amounts of frame motions will also have a substantial effect to improve a vertical scanning rate (refresh or frame rate). As it can be seen from the case of changing a frequency from 24 Hz, which is used for films, to 30 Hz for NTSC televisions, it is important to increase the vertical scanning rate X times, where X is a non-integer (i.e., X=1.5). In order to achieve this, it is more efficient to make composite images between given image frames using the information given from the image motions. Otherwise, the cumulative error will be increased significantly.